The present invention relates to a signal receiving apparatus and a related method, and more particularly to a mixer-first low-cost signal receiver, and method thereof.
In a wireless communications system, a receiver is used to receive a wireless signal having a specific bandwidth. To precisely receive the wireless signal, the receiver may need to have the ability to filter out the unwanted signal outside the specific bandwidth before converting the inputting signal into digital domain. Meanwhile, the receiver should not provide too much noise to the inputting signal. Otherwise, the signal-to-noise ratio (SNR) of the inputting signal will degrade. Conventionally, a low-noise amplifier is used to amplify the wireless signal, and a large capacitor is used to provide a sharp filtering effect for the receiver. However, the low-noise amplifier may consume a large amount of power of the receiver when the gain is high. When the gain is high, the linearity is another problem for the low-noise amplifier because the inputting signal may be distorted by the non-linear effect of the low-noise amplifier. On the other hand, the large capacitor may reduce the gain in the required in-band frequency of the receiver. In other words, the large capacitor may cause the gain response of the receiver to be too sharp such that the signal-to-noise ratio of the inputting signal degrades at the channel edge. Moreover, the large capacitor also occupies a large chip area of the receiver.
Therefore, providing a low cost receiver having flat in-band response and sharp adjacent-band rejection is an urgent problem in the field of wireless communications system.